Live center



G. H. Rwy 2,844,063

LIVE CENTER July 22, 1958 Filed Sept. 1, 1953 Z'Sheets-Sheet 1 FIG. 1

.3 7 I7 Q 6 /i/ I wrq/vrap 604/723? f/OAZST m July 22, 1958 G. H. RDHM 2,844,063

LIVE CENTER Filed Sept. 1, 1953 2 Sheets-Sheet 2 INVE/WUP 603/722? HORST 202 M,

nite 1 LIVE CENTER Giin'ter Horst Riihm, So'ntheim (Brenz), Wurttemberg, Germany I AppEicationSeptember' 1', 1953," Serial No. 377,931

Claims'priority, applicationGenn-any September 1, 1952 3 Claims.'- '(Cl. 82-'-33) States Patent so as to increase the life of the tool' as well as to im- It is another important object of the invention to provide such a bearing structure with resilient meanspermitting axial shifting of the center to compensatefor the heat expansion of theworkpiece and" to protect it from being bent or damaged thereby, as well as the center tip, its shaft, and bearing structure from being damaged by excessive stresses exerted'thereon.

Still another object of the invention is to-provide means for determiningthe amountof pressure: exerted 'by' the workpiece upon the center tip, and for determining the amount or distance which the center tip is being shifted in axial direction under the pressure of the workpiece and the cutting forces exerted'uponthe workpiece.

Still another object of the invention is to provide means for regulating or compensating the pressure-upon the center tool which has thus been'determined.

Live center tools'of'various construction have been' known which were designed toaccomplish one or the other of the abovementionedobjec'ts. However, none of these prior designs have "beencapable to achieve a combination of all these objects as shown by the present invention. For exampleylive centers have been known in which the'attempt'was madeto take up the pressure exerted upon the center point or. tip deeply within the tapered shank of'the center housing and thustospread" the forces over a series of more or less effective bearings arranged at a relatively large distance from eachother.

Other centers have been known in which resilient means' such as springs, rubber or cork cushions were provided to compensatefor the increase in pressure upon the center tip caused by the'heat expansion of the workpiece.

Still other centers, for example as shown in the United.

2,844,063 Patented July 22, 1958 "ice distribution'of forces to bearings arranged along such considerable shaft length.

It is thereforestill another object of the invention to produce a live center unit of superior construction which combines all the advantages of the. prior artv while overcoming all its individual disadvantages.

A principal feature of the invention for attaining these objects consists in a novel bearing for a live center in which thecenter shaft as wellas the annular bearings thereof are resiliently supported. in axial direction, and.

wherein the resilient means principally consist .of an annular chamber containing a suitable pressure transmitting medium such as oil or grease, small steel balls, an elastic ring, or a combination of one or more of these means.

Another .feature of .the invention consists in the provision'of a variety of means for indicating the pressure exerted upon "the center tip and the amount or distance whichthe bearings 'of'the center are shifted in axial direction, and of means for regulating such pressure or distance.

' Further objects, features, and advantages of the invention'iwill' appear from the following description thereof andthe accompanying drawings, in which Fig. l shows a longitudinal. sectionthrough a live center according to the invention;

Fig. 2 is a rear view, partly in section, of the novel unit shown in Fig.1, such sectionbeing taken along the line IIII of Fig. 1;

Fig. '3 is a fractional sectional view of a bearing structure similar'to' that shown in Figs. 1 and.2, but with a shorter center shaft therein;

Fig. '4 is a view similar to Fig. 3, but showing a modificationdesigned for a different pressure transmitting medium;

Fig. "5 is a longitudinal section, of an embodiment of the invention similar to Fig.3, but showing a different type" of pressure indicator;

Fig. "6 is'a sectional view through an embodiment of the invention with a pressure transmitting medium as shown in Fig. 4, but with another type of pressure indicatoryand Fig. 7 isamodification of the invention similar to Fig. 3, but showing still anotherj'type of pressure indicato'r.

In the drawings, the center housing includes the head lwithin which the center 2 is rotatably supported by a radial thrust bearing 3 andan axial thrust bearing 4. As shown in Fig. l, the shaft 5 of the center 2 projects deeply 'into the tapered shank 6 of the housing which is adapted to be fitted into the tailstock of the lathe or othermachine. In the embodiments of the invention shown in Figs.'3 to 7, the shaft '5 reaches approximately to the base of the head 1, and 'it is supportedat its rear end by a needle bearing 7. The socket formed in the tapered shank'6 contains at its bottom a spring 8 which presses against a plate 9 which, in turn, supports a steel ball 10 acting as a bearing-upon the rear end of the shaft 5.

A collar ll'onthe center 2 bears against a protective cover 12 which,'as shown in the drawings, together with the bearings 3 and 4 permits certain axial movement relative to the housing 1.- An annular central portion on the rear. wall of the cover 12 bears against the inner race 13 of the roller bearing?) which thus transmits the center pressure through the ball bearing 4 to a solidring 14 which is slidably supported in an annular socket '15 to act upona resilient medium l6 or 17 which'will thus be compressed by the ring.14 when pressure is exerted,

upon the center 2. Thiskresilient medium may, either at its rear side, or ofa large series of small balls 17,

The annular socket 15 is connected with a chamber 19 from which two channels 20 and 21 are leading to the- 5, and 7, the chamber 19 as well as the channels 20 and i 21 are filled with oil or grease. Channel 20 is connected to a pressure gauge 22, while channel 21 is connected to a pressure regulator 23 consisting of a ball 24 which is slidably adjustable in the pressure chamber 26 by means of a knurled screw 25.

In the modification of the invention shown in Fig. 4, the pressure transmitting medium consists of a large series of small balls 17 filling that part of the annular chamber or socket 15 which is not taken up by the ring 14 which thus acts upon the mass of balls like a piston. The adjoining chamber 19 contains a piston 27 which is slidable therein against the action of a spring 28. The remaining portion of the chamber 19 is filled with oil or grease.

In the modification of the invention shown in Fig. 5, the head 1 of the center housing is provided with a coaxial bore 29 which is connected with the annular socket 15 through the chamber 19.and the channel 20. The bore 29 contains a ball 30 and a piston 31 which are slidable therein against the action of a compression spring 32. The wall above the bore 29 is provided with a suitable slot 33 which is covered by a transparent disc or window 34 having a graduated scale marked thereon for indicating the amount which the center 2 and consequently the piston 31 are shifted relative to the housing 1.

In the modification shown in Fig. 6, similar to the embodiment of the invention shown in Fig. 4, the thrust bearing 4 acts through the ring 14 upon a pressure transmitting medium consisting of a mass of small balls 17 or a mixture of grease or oil with suchballs which fill out the part of the annular chamber 15 which is not taken up by the ring 14, as well as the extension 19 thereof which continues upwardly to form a cylindrical piston chamber 35. A piston 36 mounted on a piston rod 37 is slidably movable within chamber 35 against the action of a spring 38. A graduated scale marked on the piston rod 37 registers the amount which the center 2 is shifted relative to the housing 1 or the corresponding pressure exerted upon the center tip. a

Still another method of indicating the center pressure is shown in the embodiment of the invention shown in Fig. 7, wherein similarly to Figs. 1, 3, and the solid ring 14 transmits the pressure of the axial thrust bearing 4 to the elastic ring 16 from which the pressure is then transmitted to a piston 39 which is slidable within the piston chamber 19. One arm 40 of a suitable tracer which is pivotable about 'an axis 41 rests against the piston 39, while the other arm 42 rests against the tip 43 of a dial gauge (not shown). When the pressure upon the center 2 decreases, the tracer 40, 42 as well as the piston 39 are returned to their normal position by a spring 44 in the chamber 19.

The operation of the live center tool is as follows: The workpiece is mounted on the center tip 2 under an initial pressure which depends upon the weight, depth of cut, and the type of material of the workpiece, and the so-called mounting pressure is registered by the pressure gauge 22. If during the operation, the workpiece expands through the heat of cutting, the increase in pressure can be easily read on the gauge and reduced to normal either by an adjustment of the pressure regulator 25 or the tailstock of the machine so that the original mounting pressure as well as the same amount of friction on the center can always be maintained. Even if no measuring instrument such as a pressure gauge or other indicating means and no special pressure regulator is provided, it is always possible to obtain a balance of pressure through the resiliency of the novel bearing construction, so as to prevent undue stresses on the center bearings, the center tip, as well as the workpiece.

Although in Figs. 3 to 7, I have shown a relatively short center shaft, it is obvious by a comparison with the embodiment of the invention shown in Fig. 1 that the shaft may in any case be made of considerable length so as to extend deeply into the tapered shank of the housing which is to be fitted into the tailstock of the respective machine. Also, additional resilient bearing means of the type shown in Fig. 1 may be provided in every case to support the rear end of the center shaft 2, and such bearing may also be of a different construction than that shown. Also, the design according to the invention may easily be modified by omitting the annular ring 14 so that the rear race of the bearing 4 acts directly upon the resilient medium 16 or 17. Further, such medium may consist of different types of materials or a combination of such materials.

While the foregoing description sets forth in detail what I regard as the preferred embodiments of the invention, it is to be understood that numerous changes may be made without departing from the scope of the invention as defined in the appended claims.

Having thus described my invention, what I claim as new is:

' 1. In a live center for lathes or similar machines, the combination of a housing forming a socket with an annular groove in the bottom of said socket, a center shaft within said socket coaxially with but spaced from said groove by the inner Wall of said groove, annular hearing means in said socket between said shaft and said housing for rotatably supporting said shaft and mounted within the inner wall of said housing so as to be slideable with said shaft in axial directionthereof, an annular member adjacent said bearing means and slideable within said annular groove, thus forming a chamber, an annular cushion of plastic, resilient material within said chamber and having an annular groove therein adjacent the bottom of said chamber, said chamber having a channel extending therefrom, pressure control means and a pressure gauge communicating with saidchannel and said chamber, and a substantially fluid medium filling said groove in said cushion and being sealed therein by said cushion, said annular member being adapted to compress said cushion when an axial pressure is exerted upon said center, said cushion then transmitting said pressure to said fluid medium to be indicated by said pressure gauge and together with said cushion tending to return said shaft to its original position.

2. In a live center for lathes or similar machines, the combination of a housing forming a socket with an annular groove in the bottom of said socket, said housing having a bore centrally of and extending beyond said annular groove, a center shaft within said socket and coaxially with but spaced from said groove by the inner wall of said groove, said shaft having an extension thereon within said bore and projecting beyond said groove, annular bearing means in said socket between said shaft and said housing and mounted within the inner wall of said socket so as to be slideable with said shaft in axial direction thereof, annular bearing means between said extension and the wall of said bore for supporting the rear end of said shaft for rotary and sliding movement relative tothe wall of said bore, an annular member adjacent said bearing means and slideable within said annular groove, thus forming a chamber, an annular cushion of plastic, resilient material within said chamber, said cushion having an annular groove therein adjacent the bottom of said chamber, a substantially fluid medium filling said groove in said cushion and being sealed therein by said cushion, and pressure control means and a pressure gauge communicating with said chamber by said medium, said first bearing means being adapted to compress said cushion when an axial pressure is exerted upon said center, said cushion then transmitting said pressure through said fluid medium to said pressure gauge and control means, and, together with said medium,

also tending to return said shaft to its original position.

3. In a live center for lathes or similar machines, the combination of a housing forming a socket with an annular groove extending axially in the bottom of said socket, a center shaft within said socket coaxially with but spaced from said groove by the inner wall thereof, said center shaft extending at least into the bottom of the housing, annular bearing means in said housing between said shaft and said housing for rotatably supporting said shaft and mounted within the inner wall of said housing so as to be slidable with said shaft in axial direction thereof, said bearing means including a solid ring projecting into and slidable within said annular groove, forming a closed chamber in that groove, said bottom having a channel extending from said chamber, pressure control means and a pressure gauge communicating with said channel and said chamber, a substantially fluid medium filling said chamber and said channel and being sealed therein by said solid ring, said bearing means through said ring being adapted to press upon said medium when an axial pressure is exerted upon said center, said medium ac control means and tending to return said center to its original position.

References Cited in the file of this patent UNITED STATES PATENTS Rohm Oct. 6, Klamp Mar. 23, Weberg June 5, Galloway Jan. 1, Barto July 2, Shepard Aug. 29, Williams Oct. 17,

FOREIGN PATENTS Switzerland Dec. 15, Italy Italy Dec. 9, Italy Belgium May 15, Germany July 22,

ting upon said pressure gauge and shaft 

